RoS is an expansion, not a new game so will require D3 Vanilla in order to play. If you are interested, keep an eye out for sales. If you just want to try out the game, you can grab the starter edition or you can wait for the PTR to come out at the end of December.

As MissCheetah said, you will need to own the base version of Diablo III prior to utilizing the additional features and Crusader class offered in its expansion, Reaper of Souls.

If you haven't had a chance to try out Diablo III yet, I'd definitely encourage you to try out the Starter Edition, which is available on both PC and Mac, or the free demos available on the PlayStation 3 and XBox 360 versions of the game.

As MissCheetah said, you will need to own the base version of Diablo III prior to utilizing the additional features and Crusader class offered in its expansion, Reaper of Souls.

If you haven't had a chance to try out Diablo III yet, I'd definitely encourage you to try out the Starter Edition, which is available on both PC and Mac, or the free demos available on the PlayStation 3 and XBox 360 versions of the game.

sorry just to clarify - if a new player wants to play the expansion, without owning the original game, he would have to buy BOTH the original AND the expansion?

For the time being, this is correct.

Blizz is not going to have an all in one pack that contains everything?

If or when such a pack becomes available, we would certainly let you know, but to date, we haven't announced a bundle which includes both Diablo III as well as the upcoming expansion.